Organic light-emitting diodes (OLEDs), also known as organic electroluminescent displays (OELDs), are an optoelectronic technology that uses organic semiconductor materials to generate reversible color changes under current driving to achieve colorful displaying. Unlike a traditional display technology, the OLED display technology does not need a backlight and uses very thin organic material coating layers and glass substrates. These organic materials illuminate when a current passes through. Moreover, an OLED display screen can be made to be relatively light and thin, has a relatively great viewing angle, and can significantly save electrical power.
A basic structure of the OLEDs is a sandwich structure, which is packaged by a thin and transparent indium tin oxide (ITO) with semiconductor characteristics connected to a positive electrode of power, and another metal cathode is further added. An entire structural layer includes a hole transport layer (HTL), an electroluminescent layer (EL), and an electron transport layer (ETL). When the power is supplied to an appropriate voltage, positive electrode holes and cathode electrons are combined in a light-emitting layer to illuminate, and three primary colors of red, green, and blue (RGB) are generated according to different formulas to form a basic color. Characteristics of OLED display devices are that they emit light by themselves, unlike liquid crystal displays (LCDs) requiring a backlight, so both visibility and brightness are high. Secondly, they have low voltage demand and high power saving efficiency, plus advantages of fast response times, being light in weight, thin thickness, a simple structure, wide viewing angles, flexibility, a wide operating temperature range, and low cost. Therefore, they have always been favored by the industry, and are considered to be the most promising new generation display technologies.
Studies have shown that compositions of water vapor and oxygen in the air have a great influence on a lifespan of OLED illuminating devices. The main reasons are as follows: when the OLED illuminating devices operate, electrons are injected from a cathode, which requires that a cathode function is as low as possible, by using metal materials such as aluminum, magnesium, calcium, etc. These metal materials are generally relatively active and easily react with influent water vapor. In addition, water vapor also chemically reacts with the hole transport layer and the electron transport layer, and these reactions all cause failure of the OLED illuminating device.
OLED illuminating devices need to inject electrons from the cathode when working, which requires that a cathode work function to be the lower the better, such as metal materials such as aluminum, magnesium, and calcium, which are generally more active and easily react with the influent water vapor. In addition, water vapor also chemically reacts with the hole transport layer and the electron transport layer, and these reactions all cause failure of the OLED illuminating device. Therefore, the lifespan of the device can be greatly extended by an effective packaging of the OLED illuminating device, so that functional layers of the device are separated from the components of water vapor, oxygen, and the like in the atmosphere.
In order to protect the OLED illuminating device from water and oxygen, it is usually implemented by thin film encapsulation (TFE), but short-wavelength ultraviolet light is generated during the preparation of the TFE, so an organic layer and an inorganic layer are encapsulated on the OLED metal cathode to avoid damage of the OLED illuminating device by the ultraviolet light and to block the penetration of water, oxygen, and other components, simultaneously. However, conventional package structures and metal cathodes have relatively low heat transfer rates. Heat generated inside the OLED illuminating device cannot be transmitted to the outside in time, and the heat will accumulate inside the OLED illuminating device, and the OLED illuminating device is damaged when the heat is accumulated to a certain extent.